Stabilization of aromatic amines



United States Patent 2,927,136 STABILIZATION ()F AROMATK. AIVEINES Leslie M. Schenck, Westfieid, NJ., assignor to General Aniline & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Application August 24, 1956 Serial No. 605,944

4 Claims. (Cl. 260578) This invention relates to the stabilization of aromatic amines, and relates more particularly to the stabilization of aromtaic amines against discoloration by deterioration during storage.

Aromatic amines such as meta-chloroaniline, aniline, the toluidines and the like are normally colorless directly after preparation or distillation. However, the aromatic amines have a tendency to darken in color during storage, and this darkening is greatly accelerated when the storing is at an elevated temperature.

It is an important object of this invention to provide a process for effectively retarding the discoloration of aromatic amines during storage.

Another object of this invention is the provision of color-stable aromatic amines which are capable of being stored for an appreciable length of time without excessive discoloration.

Other objects and advantages of this invention will appear from the following description and claims.

I have found that aromatic amines which are normally colorless when prepared and have a tendency to darken in color during storage may have this tendency toward color deterioration retarded by adding thereto a small amount of stabilizing agent such as thiourea or an alkyl tin compound. While alkyl borates may also be employed as stabilizers for the aromatic amines, they are not as efiective as the thioureas or the alkyl tin compounds.

Thus, I have found that adding from 0.01 to 1.0% by weight, and preferably, 0.05 to 0.5% by weight, of a stabilizer such as ethylene thiourea, dibutyl tin oxide, dibutyl tin dilaurate, triethyl borate, tributyl borate to the aromatic amine the tendency toward color deterioration thereof during storage is substantially retarded. While this invention is applicable to any aromatic amine having a tendency to darken during storage such as, for example, aniline, alkyl anilines, halogen substituted anilines, toluidines and naphthylamines, it is particularly applicable in connection with the color stabilizing of m-chloroaniline.

The following example, which is given by way of illns tration only, is given to demonstrate the advantage of this invention.

EXAMPLE To portions of freshly distilled m-chloroaniline is added one of the stabilizing compounds, ethylenethiourea, dibutyl tin oxide, dibutyl tin laurate, triethyl borate and tributyl borate, in an amount of 0.1% by weight on the "ice Storage tests on m-chloroaniline Optical Density after storage at186 r2 Stabilizer, 0.1% Concentration 0 hours 96 hours 288 hours ntrol 3 98 Ethylene Thlonrea. 3 19 52 Dibutyl Tin Oxide 3 21 59 Dibut-yl Tin Dilanrate 3 19 68 Triethyl Borate 3 57 82 Tributyl Borate 3 50 79 1 Optical densities were determined on a General Electric Luxirneter scale reading 0-100, with distilled water used to standardize the meter at 0 reading.

It will be seen from the above table that ethylene thiourea, dibutyl tin oxide and dibutyl tin dilaurate give excellent results as color stabilizers for the aromatic amines, whereas triethyl borate and tributyl borate retard color deterioration to a much more limited extent.

It is to be understood that the foregoing detailed description is merely given by way of illustration and that many variations may be made therein without departing from the spirit of my invention.

Having described my invention, what I desire to secure by Letters Patent is:

1. Process for retarding the color deterioration of m-chloroaniline, which comprises adding to the m-chloroaniline 0.1% by weight, on the weight of the m-chloroaniline, of dibutyl tin oxide as the sole stabilizing agent.

2. Process for retarding the color deterioration of m-chloroaniline, which comprises adding to the m-chloroaniline 0.1% by weight, on the weightof the m-chloroaniline, of dibutyl tin dilaurate as the sole stabilizing agent.

3. A color stable m-chloroaniline consisting essentially of m-chloroaniline having incorporated therein 0.1%

by weight, on the weight of the m-chloroaniline, of dibutyl tin oxide.

4. A color stable m-chloroaniline consisting essentially of m-chloroaniline having incorporated therein 0.1% by weight, on the weight of the m-chloroaniline, of dibutyl tin dilaurate.

References Cited in the file of this patent UNITED STATES PATENTS 2,047,144 Kharasch July 7, 1936 2,123,928 Bousquet July 19, 1938 2,373,049 Pedersen Apr. 3, 1945 2,422,503 Smith June 17, 1947 2,655,543 Linch Oct. 13, 1953 2,691,681 Linch Oct. 12, 1954 2,789,103 Weinberg et al. Apr. 16, 1957 

1. PROCESS FOR RETARDING THE COLOR DETERIORATION OF M-CHLOROANILINE, WHICH COMPRISES ADDING TO THE M-CHLOROAMILINE 0.1% BY WEIGHT, ON THE WEIGHT OF THE M-CHLOROANILINE, OF DIBUTYL TIN OXIDE AS THE SOLE STABILIZING AGENT.
 2. PROCESS FOR RETARDING THE COLOR DETERIORATION OF M-CHLOROANILINE, WHICH COMPRISES ADDING TO THE M-CHLOROANILINE, 0.1% BY WEIGHT, ON THE WEIGHT OF THE M-CHLOROANILINE, OF DIBUTYL TIN DILAURATE AS THE SOLE STABILIZING AGENT. 